1. Field of the Invention
The invention relates to single facers for forming single-faced corrugated board and more particularly to arrangements for effecting bonding of the corrugated web to a liner web to form the single-faced board.
2. Description of the Prior Art
Single facers of the prior art, for example, that shown schematically in FIG. 1 of the accompanying drawings, include conventionally an upper corrugating roll 10 and a lower corrugating roll 12 each of which includes a plurality of longitudinally extending flutes 14 and 16 respectively. The two corrugating rolls are arranged to mesh and the web 18 to be corrugated is supplied between the meshing flutes to form the corrugations therein, the corrugated web being indicated at 20 in FIG. 1.
Conventionally a pasting roll 22, arranged to turn in a bath of paste indicated at 24, is provided for supplying paste to the tips of the corrugated web 20. A doctor roll 26 is provided to control the amount of paste supplied by the pasting roll 22 to the corrugated web 20.
Another web sheet 28, referred to hereinafter as a liner web, is supplied over a pressure roll 30 and brought into engagement with the pasted corrugated web to form the single-faced corrugated board indicated at 32. The pressure roll 30 is positioned adjacent the lower corrugating roll 12 and is arranged to apply pressure to the corrugated web and liner web to effect bonding of these two webs. Normally the upper corrugating roll 10, the lower corrugating roll 12 and the pressure roll 30 are of hollow construction and vapor or high temperature oil is introduced into the internal hollow chamber to heat these rolls and promote the corrugating of the web 18 and the bonding of the corrugated web 20 to the liner web 28.
Prior art apparatus of this type is subject to problems which are best illustrated by reference to FIGS. 2a and 2b of the accompanying drawing, both of which represent schematically the lower corrugating roll 12 and the pressure roll 30 arranged to bear thereagainst. In FIG. 2a two adjacent flutes 34 and 36 are shown in a particular position relative to the pressure roll 30. Turning now to FIG. 2b it can be seen that the two rolls 12 and 30 have moved in the direction shown by the arrows in an amount equal to half the distance between adjacent flutes, and flute 34 has moved to a position where it is disposed on a line extending between the centers of the rolls 12 and 30. It can be seen by comparison of FIGS. 2a and 2b that the aforementioned movement has caused the distance between the shafts of the lower corrugating roll 12 and the pressure roll 30 to be altered so that the distance therebetween has increased by an amount indicated by the dimension .delta. in FIG. 2b. Because of this forcible displacement and the variation in the distance between the shafts of the two rolls, the cycle of which occurs during an amount of rotation equal to the distance between two adjacent flutes, vibrations occur between the lower corrugating roll 12 and the pressure roll 30. Such relative movement of the two rolls and resulting vibrations not only cause noise but also result in breakage of the corrugated web, when it is of low quality, at the engagement point between the lower corrugating roll and the pressure roll.
In an effort to eliminate such vibration and minimize such breakage of the corrugated web the prior art structure shown in FIG. 3 was developed. The upper and lower corrugating rolls and the pasting roll and associated elements are the same as those shown in FIG. 1 and the same numerals have been applied thereto. However, in the apparatus shown in FIG. 3, a pressure member 38 has been substituted for the pressure roll 30 of the apparatus shown in FIG. 1. This pressure member 38 has a curved or arcuate surface which is opposed to the lower corrugating roll 12 and has a curvature equal to or greater than that of a line extending through the outer surface of the lower corrugating roll, that is through the tips of the flutes of the lower corrugating roll 12. With this construction, the distance between the pressure member 38 and the lower corrugating roll 12 does not vary, and the aforementioned forcible displacement and vibrations of the prior art structure of FIGS. 1 and 2 are eliminated. This can be appreciated by reference to FIG. 4 which illustrates that the distance between the pressure member 38 and the lower corrugating roll 12 does not vary between an engagement point A at the leading edge of the pressure member 38 and an engagement point B at the trailing edge of the pressure member 38, nor at any intermediate point between these two engagement points.
However, the apparatus shown in FIG. 3, while eliminating the aforementioned problem, introduces another problem in the operation of a single facer. The pressure member 38 has a length greater than the distance l between two adjacent flutes 34 and 36 shown in FIG. 4, and the pressure member 38 is fixedly positioned so that the arcuate surface thereof remains fixed while the flutes of the lower corrugating roll 12 move past the surface of the pressure member 38. As a result, a friction force occurs between the liner web 28 and the pressure member 38, and this force is applied to the joints between the liner web 28 and the corrugated web 20 between the engagement points A and B, one such joint being indicated at C in FIG. 4. The result of the application of this frictional force is to cause relative movement between the liner web 28 and the corrugated web 20 and hence to cause separation between these two webs. This results in unsatisfactory bonding and unsatisfactory single-faced corrugated board produced in the apparatus.
In accordance with the present invention, these problems and deficiencies in prior art structures have been overcome and a single facer is provided which manufactures a single-faced corrugated board in which the liner web and corrugated web are effectively bonded.
Accordingly, it is an object of this invention to provide a single facer utilizing a pressure member for effecting bonding of the liner web and corrugated web in which provision is made for minimizing the friction introduced in the area between the pressure member and the adjacent lower corrugating roll.
It is a further object of this invention to provide such an apparatus in which the friction force generated by the liner web and pressure member is reduced so that separation in the joint portions of the liner web and the corrugated web is prevented.